System and method for the treatment of hydraulic fracturing backflow water

Abstract

Hydraulic fracturing produces backflow water that is high in total dissolved solids, hardness and silica. A system to treat backflow water has an electrical separation unit and a reverse osmosis (RO) unit. The electrical separation unit may comprise an electrodialysis device (ED), an electrodialysis reversal (EDR) device or a supercapacitive desalination (SCD) device, or a combination thereof. The electrical separation unit may be combined with a precipitation unit and reduces the TDS and hardness of the backflow water. The RO unit reduces the silica concentration of the backflow water. A pre-treatment unit may further condition backflow water treated in the electrical separation unit to inhibit fouling in the RO unit. The treated backflow water may be suitable for reuse in hydraulic fracturing or discharge.

1 . A system for treating water, comprising:
 a) an electrical separation unit having an inlet and an outlet; and,   b) a reverse osmosis unit having an inlet and an outlet, wherein the inlet of the reverse osmosis unit is in communication with the outlet of the electrical separation unit.   
     
     
         2 . The system of  claim 1 , further comprising a precipitation unit in a recirculation loop associated with the electrical separation unit. 
     
     
         3 . The system of  claim 1  wherein the electrical separation unit comprises one or more of: a supercapacitor desalination device; an electrodialysis unit; and, an electrodialysis reversal unit. 
     
     
         4 . The system of  claim 3 , further comprising a precipitation unit in a recirculation loop associated with the electrical separation unit. 
     
     
         5 . The system of  claim 3 , wherein the electrical separation unit comprises a supercapacitor desalination device. 
     
     
         6 . The system of  claim 1 , further comprising a conditioning unit associated with the reverse osmosis unit. 
     
     
         7 . The system of  claim 6 , wherein the conditioning unit is downstream of the electrical separation unit and upstream of the reverse osmosis unit. 
     
     
         8 . The system of  claim 6 , wherein the conditioning unit comprises one or more of: an ion exchange unit; a softening unit; a decarbonation unit; a degasifying unit; and, an additive dosing unit. 
     
     
         9 . The system of  claim 8 , wherein the conditioning unit comprises a pH increasing additive dosing unit. 
     
     
         10 . The system of  claim 1  provided as a mobile unit. 
     
     
         11 . A process for treating water comprising steps of,
 a) electrically separating ionic species from the water; and,   b) after step a), removing silica from the water.   
     
     
         12 . The process of  claim 11  further comprising a step of precipitating the separated ionic species. 
     
     
         13 . The process of  claim 11  wherein step b) comprises passing the water through a reverse osmosis membrane filtration. 
     
     
         14 . The process of  claim 13  further comprising a step of conditioning the water for the silica removal step. 
     
     
         15 . The process of  claim 14  wherein the conditioning step comprises increasing the pH of the water. 
     
     
         16 . The system of  claim 1  wherein the water is hydraulic fracturing blowback water. 
     
     
         17 . The process of  claim 11  wherein the water is hydraulic fracturing blowback water.